Lysyl oxidase (LO or LOX) is a copper containing amine oxidase that oxidizes primary amine substrates to reactive aldehydes. LOX catalyzes oxidative deamination of peptidyl lysine and hydroxylysine residues in collagens, and peptidyl lysine residues in elastin, and aids in the formation of the extracellular matrix. The resulting peptidyl aldehydes typically condense and undergo oxidation reactions to form the lysine-derived covalent cross-links required for the normal structural integrity of the extracellular matrix. Hydrogen peroxide (H2O2) and ammonium are usually released in quantities stoichiometric with the peptidyl aldehyde product.
LOX can oxidize certain lysine residues in collagen and elastin outside of the cell; however, it may also act intracellularly, where it may regulate gene expression. In addition, LOX can induce chemotaxis of monocytes, fibroblasts and smooth muscle cells. LOX itself can be induced by a number of growth factors and steroids such as TGF-β, TNF-α and interferon (Csiszar, Prog. Nucl. Acid Res. 70:1-32 (2001)). LOX has also been implicated in diverse biological functions such as developmental regulation, tumor suppression, cell motility, and cellular senescence. The diverse role of LOX and its recently discovered amino oxidase family members, lysyl oxidase related or lysyl oxidase-like proteins (LOR or LOXL), may play important roles with respect to their intracellular and extracellular localization.
The expression or implication of LOX and LOXL in diseases may also vary. This may be due to a number of reasons, such as the difference in tissue distribution, processing, domains, regulation of activity, as well as other differences between the proteins. For example, LOX and LOXL are implicated in fibrotic diseases as both LOX and LOXL are highly expressed in myo-fibroblasts around fibrotic areas (Kagen, Pathol. Res. Pract. 190:910-919 (1994); Murawaki et al., Hepatology 14:1167-1173 (1991); Siegel et al., Proc. Natl. Acad. Sci. USA 75: 2945-2949 (1978); Jourdan Le-Saux et al., Biochem. Biophys. Res. Comm. 199:587-592 (1994); Kim et al., J. Cell Biochem. 72:181-188 (1999)). LOX and the various LOXL are also implicated in a number of cancers. For example, LOXL and LOXL4 have been shown to be epigenetically silenced and can inhibit ras/extracellular signal-regulated kinase signaling pathway in human bladder cancer (Wu et al., Cancer Res. 67:4123-4129 (2007)). Others have shown selective upregulation and amplification of the LOXL4 gene in head and neck squamous cell carcinoma (Gorough et al., J. Pathol. 212:74-82 (2007)). LOX and LOXL2 have also been implicated in a number of tumors, such as colon and esophageal cancers (Csiszar, Prog. Nucl. Acid Res. 70:1-32 (2001)). In breast cancer, LOX and the LOXL family members have been linked to cancer (Kirschmann et al., Cancer Res. 62:448-4483 (2002)).
Thus, there is a need for compositions and methods to modulate LOX and LOXL activity. One such method is through the use of RNA interference (RNAi). RNAi refers to methods of sequence-specific post-transcriptional gene silencing which is mediated by a double-stranded RNA (dsRNA) called a short interfering RNA (siRNA). RNAi is an endogenous mechanism that uses small noncoding RNAs to silence gene expression. When an siRNA is introduced into a cell, it binds to the endogenous RNAi machinery to alter the level of mRNA containing complementary sequences with high specificity. The RNAi response involves an endonuclease complex known as the RNA-induced silencing complex (RISC), which mediates cleavage of a single-stranded RNA complementary to the antisense strand of the siRNA duplex. Cleavage of the target RNA takes place in the middle of the region complementary to the antisense strand of the siRNA duplex (Elbashir et al., Genes Dev. 15:188-200, (2001)).
As a result, there is a need for compositions to modulate LOX and LOXL, such as through the use of RNAi. Methods for using such compositions to treat and diagnose conditions are also needed. The present disclosure addresses these needs and provides other advantages as well.